Vehicle security systems are widely used to deter vehicle theft, prevent theft of valuables from a vehicle, deter vandalism, and to protect vehicle owners and occupants. A typical automobile security system, for example, includes a central processor or controller connected to a plurality of vehicle sensors. The sensors, for example, may detect opening of the trunk, hood, doors, windows, and also movement of the vehicle or within the vehicle. Ultrasonic and microwave motion detectors, vibration sensors, sound discriminators, differential pressure sensors, and switches may be used as sensors. In addition, radar sensors may be used to monitor the area proximate the vehicle.
The controller typically operates to give an alarm indication in the event of triggering of a vehicle sensor. The alarm indication may typically be a flashing of the lights and/or the sounding of the vehicle horn or a siren. In addition, the vehicle fuel supply and/or ignition power may be selectively disabled based upon an alarm condition.
A typical security system also includes a receiver associated with the controller that cooperates with one or more remote transmitters typically carried by the user as disclosed, for example, in U.S. Pat. No. 4,383,242 to Sassover et al. The remote transmitter may be used to arm and disarm the vehicle security system or provide other remote control features from a predetermined range away from the vehicle.
Other vehicle security systems may be associated with the ignition of the vehicle. More particularly, one type of conventional vehicle security system includes a passive transponder either carried by the keychain or embedded in the ignition key. When the transponder is positioned adjacent the ignition switch, the transponder is inductively powered and transmits a uniquely coded signal to a receiver in the vehicle. When a properly coded transponder is detected, the vehicle engine may be allowed to start, for example. In other words, an ignition or fuel cutoff is normally operative to prevent the engine from starting or running, unless the proper transponder is sensed. Accordingly, vehicle security is increased.
The security system may have multiple transponders capable of disabling the ignition or fuel cutoff to thereby permit operation of the vehicle. These uniquely coded transponders may be added or deleted from the vehicle controller. Unfortunately, the owner of the vehicle may not know that a transponder has been added without authorization.
U.S. Pat. No. 5,513,105 to Krones, for example, discloses a vehicle security system including a so-called "computerized key" which sends a unique digitally encoded signal through a so-called "keyport" in the vehicle to a processor and controller in the vehicle. The vehicle starting is interrupted unless the proper computerized key is presented to the keyport. A valet mode is also possible wherein the computerized key is not needed. In addition, the system may be reprogrammed to accept new replacement keys. The processor and controller may be programmed to accept and recognize authorization of a plurality of computerized keys, each having individual uniquely identifying digital numbers stored therein. A program mode may be entered by presenting an authorized key for set time, then presenting new keys to be added. In the event that the memory has been filled, a long beep is indicated and the program mode is terminated. A lost key function permits a user to return the system to the program mode and thereby authorize a new set of keys to the exclusion of the previously authorized keys. Entering the lost key mode involves disconnecting the vehicle battery for a set time.
U.S. Pat. No. 5,055,701 to Takeuchi discloses a keyless entry system using a random code portion to prevent code stealing. Along these lines, U.S. Pat. No. 4,928,098 to Dannhaeuser also discloses an electronic key wherein a new coinciding code is automatically set in the infrared transmitter and receiver after each transmission and reception event. U.S. Pat. No. 5,563,579 to Carter discloses a security system for a plurality of cars, such as on a car dealer parking lot. A key storage box is mounted to the vehicle window. The storage box also includes a sensor for determining whose key is being used to unlock the box.
Unfortunately, conventional vehicle security systems using transponders have tended to attempt to increase transponder security by adding random or pseudorandom coding to the passive transponders. Unfortunately, a security threat still exists based upon unauthorized learning of a uniquely coded transponder or other token, for example. Once such a transponder or token has been learned, the would-be thief can return to the vehicle and defeat the security system.